Joint Sealant

Joint sealant materials are used to fill joints between similar or dissimilar substrates. Joint sealants seal these structure discontinuities for functional necessity. They are highly recommended in civil engineering constructions. Their function is to seal and adhere to the joint appropriate surfaces over a wide range of temperatures, environmental stress and joint movement conditions. Also their function is to prevent water moisture, and air penetration. The joint sealant must demonstrate adhesion and movement capability while resisting the effects of temperature extremes, water, sunlight, and environmental pollutants. Prior to sealant application, the joint surfaces must be clean, dry, and free of oil and grease.

Different joint sealant materials are available. The distinction of the different types from the designer’s point of view can be made on the basis of percentage elongation after weathering


Generic Type

Maximum movement capacity  (%)

Emulsion Acrylic

± 7.5

Solvent Acrylic

± 12.5

One component Polysulfide

± 12.5

Two component Polysulfide

± 25

Two component Polyurethane

± 25

Low modulus Silicone

± 25 and more


A- Care should be taken for cleaning and priming instructions to various substrates prior to sealing.

B- All joint depths should be controlled by use of polyethylene foam or bond breaker tape.

C- The expected life of the listed sealants is 10 years at least for acrylics and 20 years for others.


Azmeh Company provides two types of sealant. The first is water based Acrylic Emulsion (WT25) used for applications that require a movement capacity does not exceed ±7.5% and for joint width not exceeding 15mm. Typical uses are for sealing joints in building structures, between concrete elements, between wall and roof sections, and around door and window frames, etc. The second one is a two component Coal Tar Polyurethane (JS) recommended for civil engineering applications that require movement capacity up to ±25% and for joint width higher than 6mm. Typical uses are for subways, floors, garage forecourts, basements, reservoirs, sewage treatment plants, oil plants and in all areas exposed to fuel and chemical fumes.

Joint designs and configurations for sealant application play an important role in the successfulness of joint durability. Figures 1 and 2 show typical joint design configuration:

Conventional Moving joint

- Dimension of A&C must be at least 0.6 cm.

- Ratio of C to B should be 2 to 1 minimum.

- The joint surface should be tooled concave


Horizontal to Vertical joint

-The dimension of A & B are both greater than 0.6 cm.

-The sealant is designed to ensure positive runoff of water. 




There are different steps required for joint preparation and sealant application.

1-Substrate cleaning

Joint surfaces must be clean, dry, dust, oil, and wax free.


1-1- Non porous substrates:

Non porous substrates must be cleaned with a solvent before the sealant is applied. Non oily dirt can usually be removed with Gel Cleaner. Oily dirt generally requires a degreasing solvent such as S100.

1-2-Porous substrates:

Dusting alone may be sufficient cleaning for new porous substrates. Abrasion cleaning is used to remove surface laitance, dirt, and all previous protective coatings and sealants.



2-Primer Application:

In some cases good sealant adhesion is obtained only with the use of a primer. EPX17 is used for priming porous surfaces “concrete, brick, stone, and asbestos”. Non porous surfaces are primed by WP “Wash Primer”.

Primer can be applied by two different methods. The preferred application is to dip a clean, dry and lint-free cloth into the primer and gently wipe a thin film onto the surface. While hard to get areas and rough surfaces the primer is applied in a thin film with a clean brush.

Allow the primer to dry and the surface is now ready for application of the backer rod and sealant.



3-Backer rod application:

Using Backer rod is recommended in joint width higher than 6 mm for many purposes:

1- To control proper sealant depth, the sealant should be applied half as deep as the joint width but never less than 6mm and not over 13mm thick. The depth of the sealant is set by how deep the backer rod is placed.

2- Three-sided adhesion (adhesion to the sides and the bottom of a joint) should be prevented otherwise failure will occur when the joint moves. Because three-sided-adhesion limits the amount of movement that a joint can accept without inducing a tear

3-  Provides a firm surface to tool against forcing the sealant to the joint walls



Before sealant application, the adjacent areas of the joint require the use of a masking tape (figure 3) in order to ensure an aesthetic appearance of the joint. Then, the sealant is applied firmly in a continuous operation into the joint using a caulking gun or a putty knife and is accomplished by pushing the sealant to the joint walls to ensure complete contact with the joint sides and the backer rod.

Finally, tool the sealant with light pressure in both directions to form a concave surface before a skin begins to form. And also to force the sealant to the joint surfaces improving therefore adhesion. Masking tape should be removed immediately after tooling (before the sealant skins over).


Note: It is recommended to apply joint sealant when the joint surface is at ambient temperature and prevent temperature changes during application